When installing hydraulic systems, the installers are continuously required to thread pipes for sleeve and socket connections. As the pipe diameter changes, the thread pitch changes in accordance with the following series (which includes only the most usual diameters):
FOR DIAMETERS OF 1/4 INCH AND 3/8INCH THE PITCH IS 19 THREADS PER INCH;
FOR DIAMETERS OF 1/2 INCH AND 3/4 INCH THE PITCH IS 14 THREADS PER INCH;
FOR DIAMETERS OF 1INCH, 1 1/4 INCH, 1 1/2 INCH, 2 INCH AND UP TO 6 INCH, THE PITCH IS 11 THREADS PER INCH.
At present, the aforementioned threads are constructed using threading dies provided with cutting components knwon as chasers. These threading dies are supplied in sets to the installers and each die can only be used for one diameter. Threading dies are also available in which the position of the chasers is adjustable, so that all diameters of the same pitch can be worked, however the chasers must be changed if diameters of a different pitch are to be worked.
It is therefore apparent that even today large supplies of tool components and considerable wastage of time are involved in threading operations whenever it is required to change the working diameter.